The aims of this research project are to fully characterize the sarcomere striation pattern position and distribution throughout the volume of Ca++ tolerant isolated cardiac cells. This basic structural information will be used to evaluate the effect of osmotically induced swelling upon discrete sarcomere structure in skinned cells, the distribution and time course of activation within an individual intact cell, and the structural source and analytical limitations involved in the use of light diffractometry as a sarcomere length monitor. Ca++ tolerant isolated cells will be prepared by enzymatic digestion of rat myocardium. Optically discrete cell volumes will be sequentially imaged along lateral and focal plans of selected isolated cells with a new state of the art high-resolution direct imaging system. The A-I band striation pattern will be imaged through a high-resolution Nomarski contrast enhanced optical microscope onto an external solid state detector which is coupled on-line to a digital computer. Striation pattern images are digitally processed to determine individual striation positions throughout the small (120 x 20 um) isolated cells. Sarcomere length and distribution data will be obtained from isolated cardiac cells at rest or during paced electrical contractions in either a free state or when constrained by suction microelectrode pipetttes. These studies are intended to provide the structural framework necessary to utilize the isolated cardiac cell preparation as an interpretable model in future myocardial mechanics studies.